1. Field of the Invention
The present invention relates generally to the field of electrical inspection of large scale electronic devices and in particular to inspection of Liquid Crystal (LC) and Organic Light Emitting Diode (OLED) displays, and the optical and electronic systems used in this inspection.
2. Description of the Related Art
Liquid crystal display (LCD) panels incorporate liquid crystals that exhibit electric-field dependent light modulating properties. They are used most frequently to display images and other information in a variety of devices ranging from fax machines, laptop computer screens, to large screen, high-definition TVs. Active matrix LCD panels are complex layered structures consisting of several functional layers: a polarizing film; a TFT glass substrate incorporating thin-film transistors, storage capacitors, pixel electrodes and interconnect wiring a color filter glass substrate incorporating a black matrix and a color filter array and a transparent common electrode; an orientation film made of polyimide; and the actual liquid crystal material incorporating plastic/glass spacers to maintain proper LCD cell thickness.
LCD panels are manufactured under highly controlled conditions in a clean room environment to maximize yield. Nonetheless, many LCDs have to be discarded because of manufacturing flaws.
As stated above, in order to improve production yield of complex electronic devices, such as LCD panels, various inspection stages are performed in order to identify various defects that can occur during various stages of the fabrication process. The aforesaid inspection stages may be performed between the fabrication stages or after the completion of the entire fabrication process. One example of the aforesaid inspection process is the testing of TFT arrays used in LC and OLED displays for electrical defects. Various inspection devices are used to perform the aforesaid testing. Exemplary devices that could be used for this purpose include Array Checker AC5080 commercially available from Orbotech Ltd. of San Jose, Calif., USA. Alternatively, the TFT array testing may be performed using electron-beam inspection systems known to persons of skill in the art and commercially available.
Electrical inspection systems in general require the device under test (DUT) to be driven with electrical signals, or patterns, that facilitate the detection of defects. These signals are conveyed from a pattern generator subsystem to the DUT by means of a structure carrying probe pins that physically touch contact pads located at the periphery of the active area of the DUT. In the case of the electrical inspection of TFT arrays, one or more shorting bars (implemented on the same substrate as the array) are often disposed between the contact pads used for array test and the panel drive lines. These shorting bars are connected to a subset of drive lines (e.g., one shorting bar may be connected to every other gate line), thereby reducing the number of contacts needed, which simplified the probing assembly.
Different devices will in general have different test pad layouts. The test pad layout may depend on the size of the DUT, the distance between adjacent devices to be tested on the same substrate, the orientation of the DUT on the substrate and other factors. If different devices are to be tested on the same electrical inspection system, the probing structure must therefore be modified to conform to the configuration of the DUT. Currently, this reconfiguration of the probing structure is accomplished using a procedure which involves intensive manual labor. For example, in electrical inspection systems using manually configured probing structures, a machine operator is required to install, calibrate, and configure a new probing structure when a different circuit layout is to be tested. This process requires the testing machine to be taken down for extended periods of time, resulting in decreased machine utilization. For processes that require a process control chamber, the operator would be required to enter the chamber to perform the reconfiguration, which could result in further machine downtime while the chamber is brought back to process conditions and may expose the operator to safety hazards.
In the event that a new panel layout is to be tested, a customized probing structure must be developed at additional cost to the customer. The probing structures not being used are stored outside of the machine, which requires additional floor space for storage.